1. Field of the Invention
This invention relates to image displays such as cathode ray tubes and flat panel displays, and is addressed specifically to improved means for identifying tubes and displays and their component parts. The invention is useful in the manufacture of monochrome image displays, and color displays including those used in home entertainment television and high-definition television, and in medium-resolution and high-resolution tubes used in color monitors.
It is a requisite in the manufacturing process to be able to positively identify not only the image display itself, but also to identify and distinguish its major components during manufacture. Such identification and distinguishing is particularly important with regard to a faceplate and the associated shadow mask of a color cathode ray tube in that it is presently required that a shadow mask be "married" to a particular faceplate, and follow that faceplate through the several stages of the manufacturing process. For example, during the screening process, the faceplate is separated from the mask four times, and the faceplate and mask must be rejoined after each separation. If by accident, the faceplate is mated with another mask, the resulting tube will be inoperable. The faulty tube will then have to salvaged, a costly operation requiring disassembly of the envelope into its components.
2. Discussion of the Related Art
In U.S Pat. No. 4,374,451 to Miller, there is disclosed a method of assembling a cathode ray tube that includes a coded marking on an external surface of a part such as the faceplate. The coded marking, shown as a bar code, is machine-read, and a manufacturing process is initiated in response. To provide for permanency and resistance to the hostile manufacturing environment, the coded marks are made by erosion of the surface of the part by abrasion, or by ablation by means of a laser beam. To enhance optical contrast, a thin, light-reflective coating, or a thin black, or dark-colored undercoating may be used.
A method for ablating a coded marking into a cathode ray tube part is disclosed in U.S. Pat. No. 4,515,867 to Bleacher et al. A dark-colored undercoating topped by a light-colored coating is applied to a glass workpiece. The coatings comprise pigment particles in an alkali silicate binder. The coded marks are recessed through the coatings by ablation, as with a laser beam.
Any disturbance of the surface of a glass workpiece, whether it be by abrasion or ablation, can be the origin of surface defects which ca lead to cracking of the glass. This is true of the glass components of a cathode ray tube, which are subject to stress-inducing temperatures as high as 460 degrees C. during the manufacturing process. It is especially true of the flat tension mask (FTM) cathode ray tube faceplates which have no curvature to inherently resist vacuum-induced stresses during the heat and exhaust cycle.
In U.S. Pat. No. 5,019,004 to Steiner et al, of common ownership herewith, coded markings are applied to a glass workpiece such as a cathode ray tube faceplate by a dispenser that exudes solder glass paste (frit) to form the lines of a bar code. The coded marks are permanent and are unaffected by high temperatures, or by acidic or caustic washes used in cathode ray tube manufacture.
None of the above references however utilizes the transparent pieces available in display units to affix the indicia to an internal surface of the transparent pieces, encapsulate the indicia for permanence, and then read through the transparent piece.
Coded markings such as bar codes can also be applied to external surfaces of image displays by means of adhesive stickers, paints, inks, or decals. However, markings by such media are by nature impermanent, and vulnerable to high processing temperatures, acidic or caustic washes, and are subject to removal or dislodgment through handling or in passing through the machinery of a production line.
In the context of the present disclosure, an image display can be a monochrome or color cathode ray tube, or a flat panel display. An "indicium" (plural, indicia) is defined as information-bearing marks such as letters, numerals, or a bar code--marks that are permanent rather than transient as in the case of a television picture or the display of a symbol on a computer monitor. Indicia may convey information such as the year of manufacture of the component, the name of the manufacturer, dimensions and composition, the production run, lot number, serial number, and U.S. patent number.